This invention relates to hydraulic master cylinder assemblies and more particularly to a hydraulic master cylinder assembly incorporating switching functions.
It has become general practice in the automobile industry to interlock the operation of the engine starter motor with other controls of the motor vehicle such that the starter motor is rendered inoperative unless the transmission is in neutral or park in motor vehicles provided with an automatic transmission or, in motor vehicles provided with a foot operated clutch and a manually operated gear shift transmission, unless the transmission is in neutral and/or the clutch pedal is fully depressed to fully release the clutch. In addition, it is convenient in a motor vehicle provided with a cruise control and a mechanical clutch to shut off the operation of the cruise control upon, for example, downshifting which in turn requires release of the clutch. Specifically, it is necessary that the cruise control be disconnected even before the clutch is fully released to enable the driver to cut out the cruise control by a slight foot tap on the clutch pedal. It is also desirable, upon clutch disengagement, to generate a signal for transmission to the engine computer indicating that the torque path is going to be disengaged so that the computer may take appropriate action such as shutting down the fuel injection or reducing the fuel injection.
Many arrangements have been provided for providing switching functions in association with the master cylinder assembly to accomplish the various desired switching operations as the clutch pedal is depressed. Examples of such switches are shown for example in U.S. Pat. Nos. 4,878,041; 4,719,444; 4,742,193; 4,649,238; and 5,343,005. The switch devices shown in these prior art patents are all of the type in which the switch mounts on the push rod of the master cylinder assembly and in which the switch includes a plurality of axially spaced switches which can be sequentially actuated in response to depression of the clutch to generate a sequential series of control signals with respect to cruise control, starter interlock, fuel injection control, etc. Whereas these prior art switches have proven to be generally satisfactory, generating the required control signals in response to depression of the clutch, the use of a separate switch module on the push rod of the master cylinder adds significantly to the overall cost and complexity of the master cylinder assembly and the sequential arrangement of the various switches along the length of the switch module results in a relatively long switch assembly which is incapatible with the relatively short push rods that are found in many present day motor vehicles.
This invention is directed to the provision of an improved switching arrangement for a master cylinder assembly.
More specifically, this invention is directed to the provision of a master cylinder assembly in which the switching functions are provided integral with the master cylinder assembly.
The invention is applicable to a pressure cylinder apparatus of the type including a hydraulic cylinder structure having a cylindrical wall defining a generally closed left end and a generally open right end; a piston movable axially within the hollow of the cylinder structure; a seal structure between the piston and the cylinder structure defining a fluid pressure chamber within the cylinder on the left side of the piston and an unpressurized chamber on the right side of the piston; a fluid pressure fitting communicating with the pressure chamber for connection to a fluid pressure conduit communicating with a coacting fluid pressure device; and a piston rod extending through the open end of the cylinder and into the unpressurized chamber for connection to the right side of the piston.
According to the invention, a contact is carried by the piston at a location on the piston to the right of the seal structure and within the unpressurized chamber; a contact is disposed at an interior surface of the cylinder within the unpressurized chamber for selective coaction with the piston contact in response to axial movement of the piston in the hollow of the cylinder; and an electrical lead is connected to one of the contacts and extends to a location external to the cylinder for providing an electrical control signal generated in response to closing of the cylinder contact by the piston contact. This switching arrangement provides a switching function required in association with a typical pressure cylinder apparatus while reducing the overall cost and complexity of the total pressure cylinder apparatus and minimizing the overall size of the total pressure cylinder apparatus.
According to a further feature of the invention, a plurality of axially spaced contacts are disposed at the interior surface of the cylinder within the unpressurized chamber for selective coaction with the piston contact in response to axial movement of the piston in the hollow of the cylinder, and a plurality of electrical leads are connected to the respective cylinder contacts and extend to locations external to the cylinder for providing respective electrical control signals generated in response to selective closing of the cylinder contacts by the piston contact. This switching arrangement provides all of the switching functions required in association with a typical pressure cylinder apparatus while reducing the overall cost and complexity of the total pressure cylinder apparatus and minimizing the overall size of the total pressure cylinder apparatus.
According to a further feature of the invention, the seal structure comprises an annular elastomeric seal positioned in an annular groove provided in the interior surface of the cylinder and arranged for wiping engagement with an exterior surface of the piston as the piston moves axially in the cylinder. This arrangement maximizes the length of the unpressurized chamber in which the cylinder contacts are disposed.
According to a further feature of the invention, the cylinder is a compound structure constituted by a left cylinder structure defining the pressure chamber and a right cylinder structure coupled to the left cylinder structure and carrying the plurality of axially spaced cylinder contacts. This arrangement allows the switching functions of the apparatus to be embodied in a separate module for inventory and quality control purposes.
According to a further feature of the invention, the right cylinder structure is a compound structure constituted by a cartridge and a right cylinder member having a cylindrical wall having an open right end and including an axially extending slot opening into the hollow interior of the right cylinder and opening at the right end of the right cylinder; the cartridge is sized to fit in the slot; the axially spaced cylinder contacts are provided on an inner surface of the cartridge; and the electrical leads are carried by the cartridge. This specific arrangement allows the switching functions of the apparatus to be totally isolated from the remainder of the apparatus for inventory and quality control purposes.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.